Method and apparatus for transmitting video and graphics in a compressed form

ABSTRACT

An apparatus for compressing and transmitting both video and graphics portions of an interactive program guide (IPG). For an IPG that comprises a graphics portion and at least one video portion having audio associated with the video portion, the apparatus separately encodes the video and audio portion and the graphics portion. The video portion is slice-base encoded using a predictive encoder that produces a bitstream comprising intra-coded picture slices and predictive-coded picture slices. The graphics portion is separately slice-base encoded to produce encoded slices of the graphics image. To transmit an IPG, a transport stream is created containing the intra-coded and predicted picture streams as well as the encoded slices that comprise a graphics image that is to be included in the IPG. The receiver reassembles the components of the IPG into a comprehensive IPG.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.09/428,066, filed Oct. 27, 1999, now U.S. Pat. No. 6,651,252 whichapplication is incorporated by reference herein.

BACKGROUND OF THE DISCLOSURE

1. Field of the Invention

The invention relates to communications systems in general and, morespecifically, the invention relates to a video compression techniquesuitable for use in an interactive multimedia information deliverysystem.

2. Description of the Background Art

Over the past few years, the television industry has seen atransformation in a variety of techniques by which its programming isdistributed to consumers. Cable television systems are doubling or eventripling system bandwidth with the migration to hybrid fiber coax (HFC)cable transmission systems. Customers unwilling to subscribe to localcable systems have switched in high numbers to direct broadcastsatellite (DBS) systems. And, a variety of other approaches have beenattempted focusing primarily on high bandwidth digital technologies,intelligent two way set top boxes, or other methods of attempting tooffer service differentiated from standard cable and over the airbroadcast systems.

With this increase in bandwidth, the number of programming choices hasalso increased. Leveraging off the availability of more intelligent settop boxes, several companies have developed elaborate systems forproviding an interactive listing of a vast array of channel offerings,expanded textual information about individual programs, the ability tolook forward to plan television viewing as much as several weeks inadvance, and the option of automatically programming a video cassetterecorder (VCR) to record a future broadcast of a television program.Unfortunately, the existing program guides have several drawbacks. Theytend to require a significant amount of memory, some of them needingupwards of one megabyte of memory at the set top terminal (STT). Theyare very slow to acquire their current database of programminginformation when they are turned on for the first time or aresubsequently restarted (e.g., a large database may be downloaded to aSTT using only a vertical blanking interval (VBI) data insertiontechnique). Disadvantageously, such slow database acquisition may resultin out-of-date database information or, in the case of a pay-per-view(PPV) or video-on-demand (VOD) system, limited scheduling flexibilityfor the information provider.

Therefore, it is desirable to provide a data compression anddecompression technique that enables interactive program guides havinggraphics and video portions to be efficiently transmitted through aninteractive information distribution system.

SUMMARY OF THE INVENTION

The invention is an apparatus for compressing and transmitting bothvideo and graphics portions of an interactive program guide (IPG). Foran IPG that comprises a graphics portion and one or more video portionshaving audio associated with the video portions, the inventive systemseparately encodes the video portion and the graphics portion. The videoportion is slice-base encoded using a predictive encoder, e.g., an MPEGencoder, that produces a bitstream comprising intra-coded picture slicesand predictive-coded picture slices. The graphics portion is separatelyslice-base encoded to produce encoded slices of the graphics image. Theencoded slices of the graphics portion can be stored in a database andrecalled as needed for transmission. To transmit an IPG, a transportstream is created containing the intra-coded and predictive-coded videostreams as well as the encoded slices that comprise a graphics imagethat is to be included in the IPG. The receiver reassembles thecomponents of the IPG by decoding the slice-based streams.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the present invention can be readily understood byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 depicts an example of one frame of an interactive program guide(IPG) taken from a video sequence that can be encoded using the presentinvention;

FIG. 2 depicts a block diagram of an illustrative interactiveinformation distribution system that includes the encoding unit andprocess of the present invention;

FIG. 3 depicts a slice map for the IPG of FIG. 1;

FIG. 4 depicts a block diagram of the encoding unit of FIG. 2;

FIG. 5 depicts a block diagram of the local neighborhood network of FIG.2;

FIG. 6 depicts a matrix representation of program guide data with thedata groupings shown for efficient encoding in accordance with thepresent invention;

FIG. 7 is a diagrammatic flow diagram of a process for generating aportion of transport stream containing intra-coded video and graphicsslices;

FIG. 8 is a diagrammatic flow diagram of a process for generating aportion of transport stream containing predictive-coded video andgraphics slices;

FIG. 9 illustrates a data structure of a transport stream used totransmit the IPG of FIG. 1;

FIG. 10 is a diagrammatic flow diagram of an alternative process forgenerating a portion of transport stream containing predictive-codedvideo and graphics slices;

FIG. 11A depicts an illustration of an IPG having a graphics portion anda plurality of video portions;

FIG. 11B depicts a slice map for the IPG of FIG. 11A;

FIG. 12 is a diagrammatic flow diagram of a process for generating aportion of transport stream containing intra-coded video and graphicsslices for an IPG having a graphics portion and a plurality of videoportions;

FIG. 13 is a diagrammatic flow diagram of a process for generating aportion of transport stream containing predictive-coded video andgraphics slices for an IPG having a graphics portion and a plurality ofvideo portions;

FIG. 14 depicts a block diagram of a receiver within subscriberequipment suitable for use in an interactive information distributionsystem;

FIG. 15 depicts a flow diagram of a first embodiment of a slicerecombination process;

FIG. 16 depicts a flow diagram of a second embodiment of a slicerecombination process;

FIG. 17 depicts a flow diagram of a third embodiment of a slicerecombination process; and

FIG. 18 depicts a flow diagram of a fourth embodiment of a slicerecombination process.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures.

DETAILED DESCRIPTION

This invention is a system for generating, distributing and receiving atransport stream containing compressed video and graphics information.The invention is illustratively used to encode a plurality ofinteractive program guides (IPGs) that enable a user to interactivelyreview, preview and select programming for a television system.

The invention uses compression techniques to reduce the amount of datato be transmitted and increase the speed of transmitting program guideinformation. As such, the data to be transmitted is compressed so thatthe available transmission bandwidth is used more efficiently. Totransmit an IPG having both graphics and video, the invention separatelyencodes the graphics from the video such that the encoder associatedwith each portion of the IPG can be optimized to best encode theassociated portion. The invention illustratively uses a slice-based,predictive encoding process that is based upon the Moving PicturesExperts Group (MPEG) standard known as MPEG-2. MPEG-2 is specified inthe ISO/IEC standards 13818, which is incorporated herein by reference.

The above-referenced standard describes data processing and manipulationtechniques that are well suited to the compression and delivery ofvideo, audio and other information using fixed or variable rate digitalcommunications systems. In particular, the above-referenced standard,and other “MPEG-like” standards and techniques, compress,illustratively, video information using intra-frame coding techniques(such as run-length coding, Huffman coding and the like) and inter-framecoding techniques (such as forward and backward predictive coding,motion compensation and the like). Specifically, in the case of videoprocessing systems, MPEG and MPEG-like video processing systems arecharacterized by prediction-based compression encoding of video frameswith or without intra- and/or inter-frame motion compensation encoding.

To enhance error recovery, the MPEG-2 standard contemplates the use of a“slice layer” where a video frame is divided into one or more slices. Aslice contains one or more contiguous sequence of macroblocks. Thesequence begins and ends at any macroblock boundary within the frame. AnMPEG-2 decoder, when provided a corrupted bitstream, uses the slicelayer to avoid reproducing a completely corrupted frame. For example, ifa corrupted bitstream is decoded and the decoder determines that thepresent slice is corrupted, the decoder skips to the next slice andbegins decoding. As such, only a portion of the reproduced picture iscorrupted.

The present invention uses the slice layer for the main purpose offlexible encoding and compression efficiency in a head end centricend-to-end system. A slice-based encoding system enables the graphicsand video of an IPG to be efficiently coded and flexibly transmitted asdescribed below. Consequently, a user can easily and rapidly move fromone IPG page to another IPG page.

A. An Exemplary Interactive Program Guide

The present invention can be employed for compressing and transmittingvarious types of video frame sequences that contain graphics and videoinformation, and is particularly useful in compressing and transmittinginteractive program guides (IPG) where a portion of the IPG containsvideo (referred to herein as the video portion) and a portion of the IPGcontains a programming guide grid (referred to herein as the guideportion or graphics portion). The present invention slice-based encodesthe guide portion separately from the slice-based encoded video portion,transmits the encoded portions within a transport stream, andreassembles the encoded portions to present a subscriber (or user) witha comprehensive IPG. Through the IPG, the subscriber can identifyavailable programming and select various services provided by theirinformation service provider.

FIG. 1 depicts a frame from an illustrative IPG page 100. In thisparticular embodiment of an IPG, the guide grid information is containedin portion 102 (left half page) and the video information is containedin portion 101 (right half page). The IPG display 100 comprises a first105A, second 105B and third 105C time slot objects, a plurality ofchannel content objects 110-1 through 110-8, a pair of channel indicatoricons 141A, 141B, a video barker 120 (and associated audio barker), acable system or provider logo 115, a program description region 150, aday of the week identification object 131, a time of day object 139, anext time slot icon 134, a temporal increment/decrement object 132, a“favorites” filter object 135, a “movies” filter object 136, a “kids”(i.e., juvenile) programming filter icon 137, a “sports” programmingfilter object 138 and a VOD programming icon 133. It should be notedthat the day of the week object 131 and next time slot icon 134 maycomprise independent objects (as depicted in FIG. 1) or may beconsidered together as parts of a combined object.

A user may transition from one IPG page to another, where each pagecontains a different graphics portion 102, i.e., a different programguide graphics. The details regarding the encoding and decoding of aseries of IPG pages in accordance with the present invention areprovided below.

Details regarding the operation of the IPG page of FIG. 1, theinteraction of this page with other pages and with a user are describedin commonly assigned U.S. patent application Ser. No. 09/359,560 filedJul. 22, 1999 which is hereby incorporated herein by reference.

B. System

FIG. 2 depicts a high-level block diagram of an information distributionsystem 200, e.g., a video-on-demand system or digital cable system, thatincorporates the present invention. The system 200 contains head endequipment (HEE) 202, local neighborhood equipment (LNE) 228, adistribution network 204 (e.g., hybrid fiber-coax network) andsubscriber equipment (SE) 206. This form of information distributionsystem is disclosed in commonly assigned U.S. Pat. No. 6,253,375, issuedJun. 26, 2001. The system is known as DIVA™ provided by DIVA SystemsCorporation.

The HEE 202 produces a plurality of digital streams that contain encodedinformation in illustratively MPEG-2 compressed format. These streamsare modulated using a modulation technique that is compatible with acommunications channel 230 that couples the HEE 202 to one or more LNE(in FIG. 1, only one LNE 228 is depicted) The LNE 228 is illustrativelygeographically distant from the HEE 202. The LNE 228 selects data forsubscribers in the LNE's neighborhood and remodulates the selected datain a format that is compatible with distribution network 204. Althoughthe system 200 is depicted as having the HEE 202 and LNE 228 as separatecomponents, those skilled in the art will realize that the functions ofthe LNE may be easily incorporated into the HEE202. It is also importantto note that the presented slice-based encoding method is notconstrained to physical location of any of the components. Thesubscriber equipment (SE) 206, at each subscriber location 206 ₁, 206 ₂,. . . , 206 _(n), comprises a receiver 224 and a display 226. Uponreceiving a stream, the subscriber equipment receiver 224 extracts theinformation from the received signal and decodes the stream to producethe information on the display, i.e., produce a television program, IPGpage, or other multimedia program.

In an interactive information distribution system such as the onedescribed in commonly assigned U.S. Pat. No. 6,253,375, the programstreams are addressed to particular subscriber equipment locations thatrequested the information through an interactive menu. A relatedinteractive menu structure for requesting video-on-demand is disclosedin commonly assigned U.S. Pat. No. 6,208,335. Another example ofinteractive menu for requesting multimedia services is the interactiveprogram guide (IPG) disclosed in commonly assigned U.S. patentapplication 60/093,891, filed in Jul. 23, 1998.

To assist a subscriber (or other viewer) in selecting programming, theHEE 202 produces information that can be assembled to create an IPG suchas that shown in FIG. 1. The HEE produces the components of the IPG asbitstreams that are compressed for transmission in accordance with thepresent invention.

A video source 214 supplies the video sequence for the video portion ofthe IPG to an encoding unit 216 of the present invention. Audio signalsassociated with the video sequence are supplied by an audio source 212to the encoding and multiplexing unit 216. Additionally, a guide datasource 232 provides program guide data to the encoding unit 216. Thisdata is typically in a database format, where each entry describes aparticular program by its title, presentation time, presentation date,descriptive information, channel, and program source.

The encoding unit 216 compresses a given video sequence into one or moreelementary streams and the graphics produced from the guide data intoone or more elementary streams. As described below with respect to FIG.4, the elementary streams are produced using a slice-based encodingtechnique. The separate streams are coupled to the cable modem 222.

The streams are assembled into a transport stream that is then modulatedby the cable modem 222 using a modulation format that is compatible withthe head end communications channel 230. For example, the head endcommunications channel may be a fiber optic channel that carries highspeed data from the HEE 202 to a plurality of LNE 228. The LNE 228selects IPG page components that are applicable to its neighborhood andremodulates the selected data into a format that is compatible with aneighborhood distribution network 204. A detailed description of the LNE228 is presented below with respect to FIG. 5.

The subscriber equipment 206 contains a receiver 224 and a display 226(e.g., a television). The receiver 224 demodulates the signals carriedby the distribution network 204 and decodes the demodulated signals toextract the IPG pages from the stream. The details of the receiver 224are described below with respect to FIG. 14.

B. Encoding Unit 216

The system of the present invention is designed specifically to work ina slice-based ensemble encoding environment, where a plurality ofbitstreams are generated to compress video information using asliced-based technique. In the MPEG-2 standard, a “slice layer” may becreated that divides a video frame into one or more “slices”. Each sliceincludes one or more macroblocks, where the macroblocks areillustratively defined as rectangular groups of pixels that tile theentire frame, e.g., a frame may consist of 30 rows and 22 columns ofmacroblocks. Any slice may start at any macroblock location in a frameand extend from left to right and top to bottom through the frame. Thestop point of a slice can be chosen to be any macroblock start or endboundary. The slice layer syntax and its conventional use in forming anMPEG-2 bitstream is well known to those skilled in the art and shall notbe described herein.

When the invention is used to encode an IPG comprising a graphicsportion and a video portion, the slice-based technique separatelyencodes the video portion of the IPG and the grid graphics portion ofthe IPG. As such, the grid graphics portion and the video portion arerepresented by one or more different slices. FIG. 3 illustrates anexemplary slice division of an IPG 100 where the guide portion 102 andthe video portion 101 are each divided into N slices (e.g., g/s1 throughg/sN and v/s1 through v/sN). Each slice contains a plurality ofmacroblocks, e.g., 22 macroblocks total and 11 macroblocks in eachportion. The slices in the graphics portion are pre-encoded to form a“slice form grid page” database that contains a plurality of encodedslices of the graphics portion. The encoding process can also beperformed real-time during the broadcast process depending on thepreferred system implementation. In this way, the graphics slices can berecalled from the database and flexibly combined with the separatelyencoded video slices to transmit the IPG to the LNE and, ultimately, tothe subscribers. The LNE assembles the IPG data for the neighborhood asdescribed below with respect to FIG. 5. Although the followingdescription of the invention is presented within the context of an IPG,it is important to note that the method and apparatus of the inventionis equally applicable to a broad range of applications, such asbroadcast video on demand delivery, e-commerce, internet video educationservices, and the like, where delivery of video sequences with commoncontent is required.

As depicted in FIG. 4, the encoding unit 216 receives a video sequenceand an audio signal. The audio source comprises, illustratively, audioinformation that is associated with a video portion in the videosequence such as an audio track associated with still or moving images.For example, in the case of a video sequence representing a movietrailer, the audio stream is derived from the source audio (e.g., musicand voice-over) associated with the movie trailer.

The encoding unit 216 comprises video processor 400, a graphicsprocessor 402 and a controller 404. The video processor 400 comprises acompositor unit 406 and an encoder unit 408. The compositor unit 406combines a video sequence with advertising video, advertiser or serviceprovider logos, still graphics, animation, or other video information.The encoder unit 408 comprises one or more video encoders 410, e.g., areal-time MPEG-2 encoder and an audio encoder 412, e.g., an AC-3encoder. The encoder unit 408 produces one or more elementary streamscontaining slice-based encoded video and audio information.

The video sequence is coupled to a real time video encoder 410. Thevideo encoder then forms a slice based bitstream, e.g., an MPEG-2compliant bit stream, for the video portion of an IPG. For purposes ofthis discussion, it is assumed that the GOP structure consists of anI-picture followed by ten B-pictures, where a P-picture separates eachgroup of two B-pictures (i.e., “I-B-B-P-B-B-P-B-B-P-B-B-P-B-B”),however, any GOP structure and size may be used in differentconfigurations and applications.

The video encoder 410 “pads” the graphics portion (illustratively theleft half portion of IPG) with null data. This null data is replaced bythe graphics grid slices, at a later step, within LNE. Since the videoencoder processes only motion video information, excluding the graphicsdata, it is optimized for motion video encoding.

The controller 404 manages the slice-based encoding process such thatthe video encoding process is time and spatially synchronized with thegrid encoding process. This is achieved by defining slice start and stoplocations according to the objects in the IPG page layout and managingthe encoding process as defined by the slices. That is, the controllerselects the graphic slices to be included in the bitstream, as well asadjusts the slice boundaries.

The graphics portion of the IPG is separately encoded in the graphicsprocessor 402. The processor 402 is supplied guide data from the guidedata source (232 in FIG. 2). Illustratively, the guide data is in aconventional database format containing program title, presentationdate, presentation time, program descriptive information and the like.The guide data grid generator 414 formats the guide data into a “grid”,e.g., having a vertical axis of program sources and a horizontal axis oftime increments. One specific embodiment of the guide grid is depictedand discussed in detail above with respect to FIG. 1.

The guide grid is a video frame that is encoded using a guide encoder416 optimized for video with text and graphics content. The guideencoder 416, which can be implemented as software, slice-base encodesthe guide data grid to produce one or more bitstreams that collectivelyrepresent the entire guide data grid. The guide encoder 416 is optimizedto effectively encode the graphics and text content.

The controller 404 defines the start and stop macroblock locations foreach slice. The result is a GOP structure having intra-coded picturescontaining I-picture slices and predicted pictures containing B andP-picture slices. The I-pictures slices are separated from the predictedpicture slices. Each encoded slice is separately stored in a slice formgrid page database 418. The individual slices can be addressed andrecalled from the database 418 as required for transmission. Thecontroller 404 controls the slice-based encoding process as well asmanages the database 418.

D. Local Neighborhood Equipment (LNE) 228

FIG. 5 depicts a block diagram of the LNE 228. The LNE 228 comprises acable modem 500, slice combiner 502, a multiplexer 504 and a digitalvideo modulator 506. The LNE 228 is coupled illustratively via the cablemodem to the HEE 202 and receives a transport stream containing theencoded video information and the encoded guide data grid information.The cable modem 500 demodulates the signal from the HEE 202 and extractsthe MPEG slice information from the received signal. The slice combiner502 combines the received video slices with the guide data slices in theorder in which the decoder at receiver side can easily decode withoutfurther slice re-organization. The resultant combined slices are PIDassigned and formed into an illustratively MPEG compliant transportstream(s) by multiplexer 504. The slice-combiner (scanner) andmultiplexer operation is discussed in detail with respect to FIGS. 5-10.The transport stream is transmitted via a digital video modulator 506 tothe distribution network 204.

The LNE 228 is programmed to extract particular information from thesignal transmitted by the HEE 202., As such, the LNE can extract videoand guide data grid slices that are targeted to the subscribers that areconnected to the particular LNE. For example, the LNE 228 can extractspecific channels for representation in the guide grid that areavailable to the subscribers connected to that particular LNE. As such,unavailable channels to a particular neighborhood would not be depictedin a subscriber's IPG. Additionally, the IPG can contain targetedadvertising, e-commerce, program notes, and the like. As such, each LNEcan combine different guide data slices with different video to produceIPG screens that are prepared specifically for the subscribers connectedto that particular LNE. Other LNEs would select different IPG componentinformation that is relevant to their associated subscribers.

FIG. 6 illustrates a matrix representation 600 of a series of IPG pages.In the illustrated example, ten different IPG pages are available at anyone time period, e.g., t₁, t₂, and so on. Each page is represented by aguide portion (g) and a common video portion (v) such that a first IPGpage is represented by g1/v1, the second IPG page is represented byg2/v1 and so on. In the illustrative matrix 600, ten identical guideportions (g1-g10) are associated with a first video portion (v1). Eachportion is slice-base encoded as described above within the encodingunit (216 of FIG. 4).

FIG. 6 illustrates the assignment of PIDs to the various portions of theIPG pages. In the figure, only the content that is assigned a PID isdelivered to a receiver. The intra-coded guide portion slices g1 throughg10 are assigned to PID1 through PID10 respectively. One of the commonintra-coded video portion v1, illustratively the tenth IPG page, isassigned to PID11. In this form, substantial bandwidth saving isachieved by delivering intra-coded video portion slices v1 only onetime. Lastly, the predictive-coded slices g1/v2 through g1/v15 areassigned to PID11. As shown in the figure, a substantial bandwidthsaving is achieved by transmitting only one group of illustrativelyfourteen predicted picture slices, g1/v2 to g1/v15. This is provided bythe fact that the prediction error images for each IPG page 1 to 10through time units t2 to t15 contain the same residual images. Furtherdetails of PID assignment process is discussed in next sections.

FIG. 7 depicts a process 700 that is used to form a bitstream 710containing all the intra-coded slices encoded at a particular time t1 ofFIG. 6. At step 702, a plurality of IPG pages 702 ₁ through 702 ₁₀ areprovided to the encoding unit. At step 704, each page is slice baseencoded to form, for example, guide portion slices g1/s1 through g1/sNand video portion slices v/s1 through v/sN for IPG page 1 704 ₁. Theslice based encoding process for video and guide portions can beperformed in different forms. For example, guide portion slices can bepre-encoded by a software MPEG-2 encoder or encoded by the same encoderas utilized for encoding the video portion. If the same encoder isemployed, the parameters of the encoding process is adjusted dynamicallyfor both portions. It is important to note that regardless of theencoder selection and parameter adjustment, each portion is encodedindependently. While encoding the video portion, the encoding isperformed by assuming the full frame size (covering both guide and videoportions) and the guide portion of the full frame is padded with nulldata. This step, step 704, is performed at the HEE. At step 706, theencoded video and guide portion slices are sent to the LNE. If the LNEfunctionality is implemented as part of the HEE, then, the slices aredelivered to the LNE as packetized elementary stream format or anysimilar format as output of the video encoders. If LNE is implemented asa remote network equipment, the encoded slices are formatted in a formto be delivered over a network via a preferred method such as cablemodem protocol or any other preferred method. Once the slice-basedstreams are available in the LNE, the slice combiner at step 706 ordersthe slices in a form suitable for the decoding method at the receiverequipment. As depicted in FIG. 7( b), the guide portion and videoportion slices are ordered in a manner as if the original pictures inFIG. 7( a) are scanned from left to right and top to bottom order. Eachof the slice packets are then assigned PID's as discussed in FIG. 6 bythe multiplexer; PID1 is assigned to g1/s1 . . . g1/sn, PID2 to g2/s1 .. . g2/sn, . . . , PID10 to g10/s1 . . . g10/sn, and PID11 is assignedto v/s1 . . . v/sn. The resultant transport stream containing theintra-coded slices of video and guide portions is illustrated in FIG. 7(c). Note that based on this transport stream structure, a receivingterminal as discussed in later parts of this description of theinvention, retrieves the original picture by constructing the videoframes row-by-row, first retrieving, assuming PID1 is desired, e.g.,g1/s1 of PID1 then v/s1 of PID11, next g1/s2 of PID1 then v/s2 of PID11and so on.

FIG. 8 illustrates a process 800 for producing a bitstream 808containing the slices from the predictive-coded pictures accompanyingthe transport stream generation process discussed in FIG. 7 forintra-coded slices. As shown in FIG. 6, illustratively, only thepredicted slices belonging to IPG page 1 is delivered. Following thesame arguments of encoding process in FIG. 7, at step 802, thepredictive-coded slices are generated at the HEE independently and thenforwarded to an LNE either as local or in a remote network location. Atstep 804, slices in the predictive-coded guide and video portion slices,illustratively from time periods t2 to t15, are scanned from left toright and top to bottom in slice-combiner and complete data is assignedPID 11 by the multiplexer. Note that the guide portion slices g1/s1 tog1/sn at each time period t2 to t15 does not change from theirintra-coded corresponding values at t1. Therefore, these slices arecoded as skipped macroblocks “sK”. Conventional encoder systems do notnecessarily skip macroblocks in a region even when there is no changefrom picture to picture. In order to provide this functionality, theencoder is given the parameters for discussed slices to skip macroblockswithout any further encoding evaluations. At step 806, the slice packetsare ordered into a portion of final transport stream, first includingthe video slice packets v2/s1 . . . v2/SN to v15/s1 . . . v15/sN, thenincluding the skipped guide slices sK/s1 . . . sK/sN from t2 to t15 inthe final transport stream. FIG. 9 depicts a complete MPEG complianttransport stream 900 that contains the complete information needed by adecoder to recreate IPG pages that are encoded in accordance with theinvention. The transport stream 900 comprises the intra-coded bitstream710 of the guide and video slices (PIDS1 to 11), a plurality of audiopackets 902 identified by an audio PID, and the bitstream 806 containingthe predictive-coded slices in PID11. The rate of audio packet insertionbetween video packets is decided based on the audio and video samplingratios. For example, if audio is digitally sampled as one tenth of videosignal, then an audio packet may be introduced into the transport streamevery ten video packets. The transport stream 900 may also contain,illustratively after every 64 packets, data packets that carry to theset top terminal overlay updates, raw data, HTML, java, URL,instructions to load other applications, user interaction routines, andthe like. The data PIDs are assigned to different set of data packetsrelated to guide portion slice sets and also video portion slice sets.

FIG. 10 illustrates a process 1000, an alternative embodiment of process800 depicted in FIG. 8, for producing a predictive-coded slice bitstream1006. The process 1000, at step 1002, produces the slice base encodedpredictive-coded slices. At step 1004, the slices are scanned tointersperse the “skipped” slices (s_(k)) with the video slices (v₁). Theprevious embodiment scanned the skipped guide portion and video portionseparately. In this embodiment, each slice is scanned left to right andtop to bottom completely, including the skipped guide and video data. Assuch, at step 1008, the bitstream 1006 has the skipped guide and videoslices distributed uniformly throughout the transport stream.

The foregoing embodiments of the invention assumed that the IPG page wasdivided into one guide portion and one video portion. For example, inFIG. 1, the guide portion is the left half of the IPG page and the videoportion is the right half of the IPG page. However, the invention can beextended to have a guide portion and multiple video portions, e.g.,three. Each of the video portions may contain video having differentrates of motion, e.g., portion one may run at 30 frames per second,portions two and three may run at 2 frames per second. FIG. 11Aillustrates an exemplary embodiment of an IPG 1100 having a guideportion 1102 and three video portions 1104, 1106 and 1108. To encodesuch an IPG, each portion is separately encoded and assigned PIDs. FIG.11B illustrates an assignment map for encoding each portion of the IPGpage of FIG. 11A. The guide portion 1002 is encoded as slices g/s1through g/sN, while the first video portion 1004 is encoded as slicesv/s1 through v/sM, and the second video portion 1006 is encoded asslices j/sM+1 through j/sL, the third video portion 1008 is encoded asslices p/sL+1 through p/sN.

FIG. 12 depicts the scanning process 1200 used to produce a bitstream1210 containing the intra-coded slices. The scanning process 1200 flowsfrom left to right, top to bottom through the assigned slices of FIG.11B. PIDs are assigned, at step 1202, to slices 1 to M; at step 1204, toslices M+1 to L; and, at step 1206, to slices L+1 to N. As the encodedIPG is scanned, the PIDS are assigned to each of the slices. The guideportion slices are assigned PIDS 1 through 10, while the first videoportion slices are assigned PID11, the second video portion slices areassigned PID12 and the third video portion slices are assigned PID13.The resulting video portion of the bitstream 1210 contains the PIDS forslices 1-M, followed by PIDS for slices M+1 to L, and lastly by the PIDSfor L+1 to N.

FIG. 13 depicts a diagrammatical illustration of a process 1300 forassigning PIDS to the predictive-coded slices for the IPG of FIG. 11A.The scanning process 1300 is performed, at step 1302, from left toright, top to bottom through the V, J and P predicted encoded slices andPIDS are assigned where the V slices are assigned PID11, the J slicesare assigned PID 12 and the P slices are assigned PID13. After the videoportion predicted encoded slices have assigned PIDs, the process 1300,at step 1304, assigns PIDs to the skipped slices. The skipped guideslices vertically corresponding to the V slices are assigned PID11, theskipped slices vertically corresponding to the J slices are assignedPID12 and the skipped slices vertically corresponding to the P slicesare assigned PID13. At step 1308, the resulting predictive-codedbitstream 1312 comprises the predicted video slices in portion 1306 andthe skipped slices 1310. The bitstream 1210 of intra-coded slices andthe bitstream 1312 of predictive-coded slices are combined into atransport stream having a form similar to that depicted in FIG. 9.

Guide pages (video PIDs for groups of slices) can not be changedseamlessly using a standard channel change by the receiver switchingfrom PID to PID directly, because such an operation flushes the videoand audio buffers and typically gives half a second blank screen.

To have seamless decoder switching, a splice countdown (or random accessindicator) packet is employed at the end of each video sequence toindicate the point at which the video should be switched from one PID toanother.

Using the same profile and constant bit rate coding for the graphicsencoding units, the generated streams for different IPG pages are formedin a similar length compared to each other. This is due to the fact thatguide pages are almost identical differing only in the characters. Inthis way, while streams are generated having nearly identical lengths,the streams are not exactly the same length. Thus, a finer adjustment isrequired to synchronize the beginnings and ends of each sequence acrossall guide slices in order for the countdown switching to work.

The invention provides the act of synchronization of a plurality ofstreams that provides seamless switching at the receiver.

Three methods are provided for that purpose:

First, for each sequence the multiplexer in the LNE identifies thelength of the longest guide page for that particular sequence, and thenadds sufficient null packets to the end of each other guide page so thatall the encoded guide page slices become the same length. Then, themultiplexer adds the switching packets at the end of the sequence, afterall the null packets.

The second method requires buffering of all the packets for all guidepage slices for each sequence. If this is allowed in the consideredsystem, then the packets can be ordered in the transport stream suchthat the packets for each guide page slice appear at slightly higher orlower frequencies, so that they all finish at the same point. Then, theswitching packets are added by the multiplexer in the LNE at the end ofeach stream without the null padding.

A third method is to start each sequence together, and then wait untilall the packets for all the guide page slices have been generated. Oncethe generation of all packets is completed, switching packets are placedin the streams at the same time and point in each stream.

Depending on the implementation of decoder units within the receiver andrequirements of the considered application, each one of the methods canbe applied with advantages. For example, the first method, which isnull-padding, can be applied to avoid bursts of N packets of the samePID into a decoder's video buffer faster than the MPEG specified rate(e.g., 1.5 Mbit).

The teachings of the above three methods can be extended apply tosimilar synchronization problems and to derive similar methods forensuring synchronization during stream switching.

E. Receiver 224

FIG. 14 depicts a block diagram of the receiver 224 (also known as a settop terminal (STT) or user terminal) suitable for use in producing adisplay of an IPG in accordance with the present invention. The STT 224comprises a tuner 1410, a demodulator 1420, a transport demultiplexer1430, an audio decoder 1440, a video decoder 1450, an on-screen displayprocessor (OSD) 1460, a frame store memory 1462, a video compositor 1490and a controller 1470. User interaction is provided via a remote controlunit 1480. Tuner 1410 receives, e.g., a radio frequency (RF) signalcomprising, for example, a plurality of quadrature amplitude modulated(QAM) information signals from a downstream (forward) channel. Tuner1410, in response to a control signal TUNE, tunes a particular one ofthe QAM information signals to produce an intermediate frequency (IF)information signal. Demodulator 1420 receives and demodulates theintermediate frequency QAM information signal to produce an informationstream, illustratively an MPEG transport stream. The MPEG transportstream is coupled to a transport stream demultiplexer 1430.

Transport stream demultiplexer 1430, in response to a control signal TDproduced by controller 1470, demultiplexes (i.e., extracts) an audioinformation stream A and a video information stream V. The audioinformation stream A is coupled to audio decoder 1440, which decodes theaudio information stream and presents the decoded audio informationstream to an audio processor (not shown) for subsequent presentation.The video stream V is coupled to the video decoder 1450, which decodesthe compressed video stream V to produce an uncompressed video stream VDthat is coupled to the video compositor 1490. OSD 1460, in response to acontrol signal OSD produced by controller 1470, produces a graphicaloverlay signal VOSD that is coupled to the video compositor 1490. Duringtransitions between streams representing the user interfaces, buffers inthe decoder are not reset. As such, the user interfaces seamlesslytransition from one screen to another.

The video compositor 1490 merges the graphical overlay signal VOSD andthe uncompressed video stream VD to produce a modified video stream(i.e., the underlying video images with the graphical overlay) that iscoupled to the frame store unit 1462. The frame store unit 1462 storesthe modified video stream on a frame-by-frame basis according to theframe rate of the video stream. Frame store unit 1462 provides thestored video frames to a video processor (not shown) for subsequentprocessing and presentation on a display device.

Controller 1470 comprises a microprocessor 1472, an input/output module1474, a memory 1476, an infrared (IR) receiver 1475 and supportcircuitry 1478. The microprocessor 1472 cooperates with conventionalsupport circuitry 1478 such as power supplies, clock circuits, cachememory and the like as well as circuits that assist in executing thesoftware routines that are stored in memory 1476. The controller 1470also contains input/output circuitry 1474 that forms an interfacebetween the controller 1470 and the tuner 1410, the transportdemultiplexer 1430, the onscreen display unit 1460, the back channelmodulator 1495, and the remote control unit 1480. Although thecontroller 1470 is depicted as a general purpose computer that isprogrammed to perform specific interactive program guide controlfunction in accordance with the present invention, the invention can beimplemented in hardware as an application specific integrated circuit(ASIC). As such, the process steps described herein are intended to bebroadly interpreted as being equivalently performed by software,hardware, or a combination thereof.

In the exemplary embodiment of FIG. 14, the remote control unit 1480comprises an 8-position joy stick, a numeric pad, a “select” key, a“freeze” key and a “return” key. User manipulations of the joy stick orkeys of the remote control device are transmitted to a controller via aninfra red (IR) link. The controller 1470 is responsive to such usermanipulations and executes related user interaction routines 1400, usesparticular overlays that are available in an overlay storage 1479. Afterthe signal is tuned and demodulated, the video streams are recombinedvia stream processing routine 1402 to form the video sequences that wereoriginally compressed. The processing unit 1402 employs a variety ofmethods to recombine the slice-based streams, including, using PIDfilter 1404, demultiplexer 1430, as discussed in the next sections ofthis disclosure of the invention. Note that the PID filter implementedillustratively as part of the demodulator is utilized to filter theundesired PIDs and retrieve the desired PIDs from the transport stream.The packets to be extracted and decoded to form a particular IPG areidentified by a PID mapping table (PMT) 1477. After the streamprocessing unit 1402 has processed the streams into the correct order(assuming the correct order was not produced in the LNE), the slices aresent to the MPEG decoder 1450 to generate the original uncompressed IPGpages. If an exemplary transport stream with two PIDs as discussed inprevious parts of the this disclosure, excluding data and audio streams,is received, then the purpose of the stream processing unit 1402 is torecombine the intra-coded slices with their correspondingpredictive-coded slices in the correct order before the recombinedstreams are coupled to the video decoder. This complete process isimplemented as software or hardware. In the illustrated IPG page slicestructure, only one slice is assigned per row and each row is dividedinto two portions, therefore, each slice is divided into guide portionand video portion. In order for the receiving terminal to reconstructthe original video frames, one method is to construct a first row fromits two slices in the correct order by retrieving two correspondingslices from the transport stream, then construct a second row from itstwo slices, and so on. For this purpose, a receiver is required toprocess two PIDs in a time period. The PID filter can be programmed topass two desired PIDs and filter out the undesired PIDs. The desiredPIDs are identified by the controller 1472 after the user selects an IPGpage to review. A PID mapping table (1477 of FIG. 14) is accessed by thecontroller 1472 to identify which PIDS are associated with the desiredIPG. If a PID filter is available in the receiver terminal, then it isutilized to receive two PIDs containing slices for guide and videoportions. The demultiplexer then extracts packets from these two PIDsand couples the packets to the video decoder in the order in which theyarrived. If the receiver does not have an optional PID filter, then thedemultiplexer performs the two PID filtering and extracting functions.Depending on the preferred receiver implementation, the followingmethods are provided in FIGS. 15-18 to recombine and decode slice-basedstreams.

E1. Recombination Method 1

In this first method, intra-coded slice-based streams (I-streams) andthe predictive-coded slice-based streams (PRED streams) to be recombinedkeep their separate PID's until the point where they must bedepacketized. The recombination process is conducted within thedemultiplexer 1430 of the subscriber equipment For illustrativepurposes, assuming a multi-program transport stream with each programconsisting of I-PIDs for each intra-coded guide slice, I-PIDs for theintra-coded video slices, one PRED-PID for predicted guide and video, anaudio-PID, and multiple data-PIDs, any packet with a PID that matchesany of the PID's within the desired program (as identified in a programmapping table) are depacketized and the payload is sent to theelementary stream video decoder. Payloads are sent to the decoder inexactly in the order in which the packets arrive at the demultiplexer.

FIG. 15 is a flow diagram of the first packet extraction method 1500.The method starts at step 1505 and proceeds to step 1510 to wait for(user) selection of an I-PID to be received. The I-PID, as the firstpicture of a stream's GOP, represents the stream to be received.However, since the slice-based encoding technique assigns two or moreI-PIDS to the stream (i.e., I-PIDs for the guide portion and for one ormore video portions), the method must identify two or more I-PIDs. Upondetecting a transport packet having the selected I-PIDs, the method 1500proceeds to step 1515.

At step 1515, the I-PID packets (e.g., packets having PID-1 and PID-11)are extracted from the transport stream, including the headerinformation and data, until the next picture start code. The headerinformation within the first-received I-PID access unit includessequence header, sequence extension, group start code, GOP header,picture header, and picture extension, which are known to a reader thatis skilled in MPEG-1 and MPEG-2 compression standards. The headerinformation in the next I-PID access units that belongs to the secondand later GOP's includes group start code, picture start code, pictureheader, and extension. The method 1500 then proceeds to step 1520 wherethe payloads of the packets that includes header information related tovideo stream and I-picture data are coupled to the video decoder 1550 asvideo information stream V. The method 1500 then proceeds to step 1525.

At step 1525, the predicted picture slice-based stream packets PRED-PID,illustratively the PID-11 packets of fourteen predicted pictures in aGOP of size fifteen, are extracted from the transport stream. At step1530, the payloads of the packets that includes header informationrelated to video stream and predicted-picture data are coupled to thevideo decoder 1550 as video information stream V. At the end of step1530, a complete GOP, including the I-picture and the predicted-pictureslices, are available to the video decoder 1550. As the payloads aresent to the decoder in exactly in the order in which the packets arriveat the demultiplexer, the video decoder decodes the recombined streamwith no additional recombination process. The method 1500 then proceedsto step 1535.

At step 1535, a query is made as to whether a different I-PID isrequested, e.g., new IPG is selected. If the query at step 1535 isanswered negatively, then the method 1500 proceeds to step 1510 wherethe transport demultiplexer 1530 waits for the next packets having thePID of the desired I-picture slices. If the query at step 1535 isanswered affirmatively, then the PID of the new desired I-picture slicesis identified at step 1540 and the method 1500 returns to step 1510.

The method 1500 of FIG. 15 is used to produce a conformant MPEG videostream V by concatenating a desired I-picture slices and a plurality ofP- and/or B-picture slices forming a pre-defined GOP structure.

E2. Recombination Method 2

The second method of recombining the video stream involves themodification of the transport stream using a PID filter. A PID filter1404 can be implemented as part of the demodulator 1420 of FIG. 14 or aspart of demultiplexer.

For illustrative purposes, assuming a multi-program transport streamwith each program consisting of an I-PIDs for both video and guide,PRED-PID for both video and guide, audio-PID, and data-PID, any packetwith a PID that matches any of the PIDs within the desired program asidentified by the program mapping table to be received have its PIDmodified to the lowest video PID in the program (the PID which isreferenced first in the program's program mapping table (PMT)). Forexample, in a program, assuming that a guide slice I-PID is 50, thevideo slice I-PID is 51 and PRED-PID is 52. Then, the PID-filtermodifies the video I-PID and the PRED-PID as 50 and thereby, I- andPredicted-Picture slice access units attain the same PID number andbecome a portion of a common stream.

As a result, the transport stream output from the PID filter contains aprogram with a single video stream, whose packets appear in the properorder to be decoded as valid MPEG bitstream.

Note that the incoming bit stream does not necessarily contain anypackets with a PID equal to the lowest video PID referenced in theprograms PMT. Also note that it is possible to modify the video PID's toother PID numbers than lowest PID without changing the operation of thealgorithm.

When the PID's of incoming packets are modified to match the PID's ofother packets in the transport stream, the continuity counters of themerged PID's may become invalid at the merge points, due to each PIDhaving its own continuity counter. For this reason, the discontinuityindicator in the adaptation field is set for any packets that mayimmediately follow a merge point. Any decoder components that check thecontinuity counter for continuity is required to correctly process thediscontinuity indicator bit.

FIG. 16 illustrates the details of this method, in which, it starts atstep 1605 and proceeds to step 1610 to wait for (user) selection of twoI-PIDs, illustratively two PIDs corresponding to guide and video portionslices, to be received. The I-PIDs, comprising the first picture of astream's GOP, represents the two streams to be received. Upon detectinga transport packet having one of the selected I-PIDs, the method 1600proceeds to step 1615.

At step 1615, the PID number of the I-stream is re-mapped to apredetermined number, PID*. At this step, the PID filter modifies allthe PID's of the desired I-stream packets to PID*. The method thenproceeds to step 1620, wherein the PID number of the predicted pictureslice streams, PRED-PID, is re-mapped to PID*. At this step, the PIDfilter modifies all the PID's of the PRED-PID packets to PID*. Themethod 1600 then proceeds to step 1625.

At step 1625, the packets of the PID* stream are extracted from thetransport stream by the demultiplexer. The method 1600 then proceeds tostep 1630, where the payloads of the packets that includes video streamheader information and I-picture and predicted picture slices arecoupled to the video decoder as video information stream V. Note thatthe slice packets are ordered in the transport stream in the same orderas they are to be decoded, i.e., a guide slice packets of first rowfollowed by video slice packets of first row, second row, and so on. Themethod 1600 then proceeds to 1635.

At step 1635, a query is made as to whether a different set of (two)I-PIDs are requested. If the query at step 1635 is answered negatively,then the method 1600 proceeds to step 1610 where the transportdemultiplexer waits for the next packets having the identified I-PIDs.If the query at step 1635 is answered affirmatively, then the two PIDsof the new desired I-picture is identified at step 1640 and the method1600 returns to step 1610.

The method 1600 of FIG. 16 is used to produce a conformant MPEG videostream by merging the intra-coded slice streams and predictive-codedslice streams before the demultiplexing process.

E3. Recombination Method 3

The third method accomplishes MPEG bitstream recombination by usingsplicing information in the adaptation field of the transport packetheaders by switching between video PIDs based on splice countdownconcept.

In this method, the MPEG streams signal the PID to PID switch pointsusing the splice countdown field in the transport packet header'sadaptation field. When the PID filter is programmed to receive one ofthe PIDs in a program's PMT, the reception of a packet containing asplice countdown value of 0 in its header's adaptation field causesimmediate reprogramming of the PID filter to receive the other videoPID. Note that a special attention to splicing syntax is required insystems where splicing is used also for other purposes.

FIG. 17 illustrates the details of this method, in which, it starts atstep 1705 and proceeds to step 1710 to wait for (user) selection of twoI-PIDs to be received. The I-PIDs, comprising the first picture of astream's GOP, represents the stream to be received. Upon detecting atransport packet having one of the selected I-PIDs, the method 1700proceeds to step 1715.

At step 1715, the I-PID packets are extracted from the transport streamuntil, and including, the I-PID packet with slice countdown value ofzero. The method 1700 then proceeds to step 1720 where the payloads ofthe packets that includes header information related to video stream andI-picture slice data are coupled to the video decoder as videoinformation stream V. The method 1700 then proceeds to step 1725.

At step 1725, the PID filter is re-programmed to receive the predictedpicture packets PRED-PID. The method 1700 then proceeds to 1730. At step1730, the predicted stream packets, illustratively the PID11 packets ofpredicted picture slices, are extracted from the transport stream. Atstep 1735, the payloads of the packets that includes header informationrelated to video stream and predicted-picture data are coupled to thevideo decoder. At the end of step 1735, a complete GOP, including theI-picture slices and the predicted-picture slices, are available to thevideo decoder. As the payloads are sent to the decoder in exactly in theorder in which the packets arrive at the demultiplexer, the videodecoder decodes the recombined stream with no additional recombinationprocess. The method 1700 then proceeds to step 1740.

At step 1740, a query is made as to whether a different I-PID set (two)is requested. If the query at step 1740 is answered negatively, then themethod 1700 proceeds to step 1750 where the PID filter is re-programmedto receive the previous desired I-PIDs. If answered affirmatively, thenthe PIDs of the new desired I-picture is identified at step 1745 and themethod proceeds to step 1750, where the PID filter is re-programmed toreceive the new desired I-PIDs. The method then proceeds to step 1745,where the transport demultiplexer waits for the next packets having thePIDs of the desired I-picture.

The method 1700 of FIG. 17 is used to produce a conformant MPEG videostream, where the PID to PID switch is performed based on a splicecountdown concept. Note that the slice recombination can also beperformed by using the second method where the demultiplexer handles thereceiving PIDs and extraction of the packets from the transport streambased on the splice countdown concept. In this case, the same process isapplied as FIG. 17 with the difference that instead of reprogramming thePID filter after “0” splice countdown packet, the demultiplexer isprogrammed to depacketize the desired PIDs.

E4. Recombination Method 4

For the receiving systems that do not include a PID filter and for thosereceiving systems in which the demultiplexer can not process two PIDsfor splicing the streams, a fourth method presented herein provides thestream recombination. In a receiver that cannot process two PIDS, two ormore streams with different PIDs are spliced together via an additionalsplicing software or hardware and can be implemented as part of thedemultiplexer. The process is described below with respect to FIG. 18.The algorithm provides the information to the demultiplexer about whichPID to be spliced to as the next step. The demultiplexer processes onlyone PID but a different PID after the splice occurs.

FIG. 18 depicts a flow diagram of this fourth process 1800 forrecombining the IPG streams. The process 1800 begins at step 1801 andproceeds to step 1802 wherein the process defines an array of elementshaving a size that is equal to the number of expected PIDs to bespliced. It is possible to distribute splice information in a picture asdesired according to slice structure of the picture and the desiredprocessing form at the receiver. For example, in the slice based streamsdiscussed in this invention, for an I picture, splice information may beinserted into slice row portions of guide and video data. At step 1804,the process initializes the video PID hardware with for each entry inthe array. At step 1810, the hardware splice process is enabled and thepackets are extracted by the demultiplexer. The packet extraction mayalso be performed at another step within the demultiplexer. At step1812, the process checks a hardware register to determine if a splicehas been completed. If the splice has occurred, the process, at step1814, disables the splice hardware and, at step 1816, sets the video PIDhardware to the next entry in the array. The process then returns alongpath 1818 to step 1810. If the splice has not occurred, the processproceeds to step 1820 wherein the process waits for a period of time andthen returns along path 1822 to step 1812.

In this manner, the slices are spliced together by the hardware withinthe receiver. To facilitate recombining the slices, the receiver is sentan array of valid PID values for recombining the slices through a userdata in the transport stream or another communications link to the STTfrom the HEE. The array is updated dynamically to ensure that thecorrect portions of the IPG are presented to the user correctly. Sincethe splice points in slice based streams may occur at a frequent level,a software application may not have the capability to control thehardware for splicing operation as discussed above. If this is the case,then, firmware is dedicated to control the demodulator hardware forsplicing process at a higher rate than a software application canhandle.

F. Example: Interactive Program Guide

The video streams representing the IPG may be carried in a singletransport stream or multiple transport streams, within the form of asingle or multi-programs as discussed below with respect to thedescription of the encoding system. A user desiring to view the next 1.5hour time interval (e.g., 9:30-11:00) may activate a “scroll right”object (or move the joystick to the right when a program within programgrid occupies the final displayed time interval). Such activationresults in the controller of the STT noting that a new time interval isdesired. The video stream corresponding to the new time interval is thendecoded and displayed. If the corresponding video stream is within thesame transport stream (i.e., a new PID), then the stream is immediatelydecoded and presented. If the corresponding video stream is within adifferent transport stream, then the related transport stream isextracted from the broadcast stream and the related video stream isdecoded and presented. If the corresponding transport stream is within adifferent broadcast stream, then the related broadcast stream is tuned,the corresponding transport stream is extracted, and the desired videostream is decoded and presented.

It is important to note that each extracted video stream is associatedwith a common audio stream. Thus, the video/audio barker function of theprogram guide is continuously provided, regardless of the selected videostream. Also note that the teachings of the invention is equallyapplicable to systems and user interfaces that employs multiple audiostreams.

Similarly, a user interaction resulting in a prior time interval or adifferent set of channels results in the retrieval and presentation of arelated video stream. If the related video stream is not part of thebroadcast video streams, then a pointcast session is initiated. For thispurpose, the STT sends a request to the head end via the back channelrequesting a particular stream. The head end then processes the request,retrieves the related guide and video streams from the informationserver, incorporates the streams within a transport stream as discussedabove (preferably, the transport stream currently being tuned/selectedby the STT) and informs the STT which PIDs should be received, and fromwhich transport stream should be demultiplexed. The STT then extractsthe related PIDs for the IPG. In the case of the PID being within adifferent transport stream, the STT first demultiplexes thecorresponding transport stream (possibly tuning a different QAM streamwithin the forward channel).

Upon completion of the viewing of the desired stream, the STT indicatesto the head end that it no longer needs the stream, whereupon the headend tears down the pointcast session. The viewer is then returned to thebroadcast stream from which the pointcast session was launched.

Although various embodiments which incorporate the teachings of thepresent invention have been shown and described in detail herein, thoseskilled in the art can readily devise many other varied embodiments thatstill incorporate these teachings. An important note is that the methodand apparatus described herein is applicable to any number of sliceassignments to a video frame and any type of slice structures. Thepresented algorithms are also applicable to any number of PIDassignments to intra-coded and predictive-coded slice based streams. Forexample, multiple PIDs can be assigned to the predictive-coded sliceswithout loss of generality. Also note that the method and apparatusdescribed herein is fully applicable picture based encoding by assigningeach picture only to a one slice, where each picture is encoded then asa full frame instead of multiple slices.

1. An encoder apparatus comprising: a video processor for encoding avideo sequence; a graphics processor for producing a plurality ofencoded graphics slices; means, coupled to said video processor and saidgraphics processor, for selectively producing for transmission abitstream comprising said encoded video, associated encoded audio, andsaid encoded graphics slices; and a controller, coupled to said videoprocessor and said graphics processor, for selecting the graphics slicesto be included in said bitstream and for adjusting the slice boundaries.2. The encoder apparatus of claim 1 wherein said video processorcomprises a video encoder and an audio encoder.
 3. The encoder apparatusof claim 1 wherein said graphics processor comprises a database forstoring said graphics slices.
 4. The encoder apparatus of claim 1wherein said video is a video portion of an interactive program guideand said encoded graphics slices represent a plurality of guide portionsfor said interactive program guide.
 5. An apparatus for distributing aninteractive program guide comprising: an encoder, for encoding at leastone video sequence having associated audio as an encoded audio and videoportion, and guide graphics as an encoded guide graphics portion, saidencoder comprising an audio encoder, a video processor and a graphicsprocessor, wherein said video processor comprises a compositor unit forreceiving video information and an encoder unit coupled to saidcompositor unit; at least one modem, for transmitting said encoded videoand guide graphics portions through a head end channel; localneighborhood equipment, coupled to said head end channel, for selectingsaid encoded video portion and said encoded guide graphics portion andproducing a transport stream comprising said encoded video portion andsaid encoded guide graphics portion; a network, for carrying saidtransport stream to at least one receiver; and at least one receiver,coupled to said network, for processing said transport stream to form aninteractive program guide.
 6. The apparatus of claim 5 wherein saidgraphics processor comprises: a guide data grid generator for receivingguide information; a guide encoder coupled to said guide data gridgenerator; and a slice form grid page database coupled to said guideencoder.
 7. The apparatus of claim 5 wherein said encoder produces aplurality of encoded video portions and a plurality of encoded guidegraphics portions that are made available to said local neighborhoodequipment.
 8. The apparatus of claim 7 wherein said local neighborhoodequipment further comprises: a modem; a slice combiner; a multiplexer;and modulator.
 9. The apparatus of claim 1 wherein said video processingcomprises a compositor unit; and an encoder unit.
 10. An apparatus fordistributing an interactive program guide (IPG) comprising: an encoderassembly having a video processor for encoding at least one videosequence of said IPG and audio associated with said video sequence as anencoded video and audio portion, and a graphics processor for encodingguide graphics of said IPG as an encoded guide graphics portion; meansfor selecting said encoded video and audio portion and said encodedguide graphics portion, and producing a transport stream comprising saidencoded video and audio portion and said encoded guide graphics portion;a network for carrying said transport stream to at least one receiver;and at least one receiver, coupled to said network, for processing saidtransport stream to form an interactive program guide; wherein saidgraphics processor comprises: a guide data grid generator; a guideencoder; and a slice form grid page database.
 11. The apparatus of claim10, wherein said encoder assembly produces a plurality of encoded videoand audio portions and a plurality of encoded guide graphics portionsthat are made available to said local neighborhood equipment.